State-of-the-art distributed power devices rely on hydraulics or electromagnetic actuation. Hydraulic actuation is reliable towards mechanical jam, but has fundamentally limited dynamic response and efficiency. Furthermore, implementation of hydraulic systems into commercial applications may be problematic as hydraulics are prone to leakage, leading to increased maintenance costs. Moreover, hydraulic actuation is hardware intensive.
Electromagnetic actuation offers a clean alternative to hydraulic actuation. For high dynamic applications, the most common form of electromechanical actuation is found in direct-drive motors, which are prohibitively heavy. Device weight can be considerably reduced by providing a reduction ratio between the motor and the end-effector. Indeed, when coupled to reduction gearboxes, electromechanical actuators are lighter and less expensive than direct drive solutions, but their high output inertia, friction and backlash may diminish their dynamic performance.
MR fluid clutch apparatuses are known as useful apparatuses for transmitting motion from a drive shaft with precision and accuracy, among other advantages, which could enhance the performance of electromechanical actuation systems.
MR fluid is known to permanently change properties over time. These changes may include, non-exhaustively, a change in viscosity, a change in the ability to transmit a shear stress in function of the magnetic flux density in the MR fluid, and a change of magnetic permeability. One factor contributing to the change of properties is the energy dissipated in the fluid when the fluid is solicited in a shear situation. A shear situation of the fluid occurs when torque is transmitted by the MR fluid clutch apparatus while an angular speed difference is present between the input and the output of the MR fluid clutch apparatus. In this condition, the apparent yield shear stress of the MR fluid in the interface between the input and the output of the MR fluid clutch apparatus controls the torque transmitted from the input of the MR fluid clutch apparatus to its output. In such a shear situation, the MR fluid absorbs energy that may be proportional to the speed difference and the torque transmitted from the input to the output. The higher the transmitted torque of the MR fluid clutch apparatus and the higher the angular speed between the input rotor and the output rotor, the more energy may be dissipated in the MR fluid and the greater the properties of the MR fluid may change over time.